1. Field of the Invention
The present invention relates to an axial fan and a slide mold used in manufacturing an axial fan.
2. Description of the Related Art
Axial fans with housings that include slits have been known. For example, WO 2009/057063 discloses one such axial fan. This axial fan includes an impeller in which a plurality of blades is arranged in a circumferential direction about a central axis, and a housing arranged radially outward from the impeller to circumferentially surround the impeller. The housing includes a plurality of slits that are arranged in the circumferential direction and arranged to extend through the housing from an inner circumferential surface to an outer circumferential surface thereof.
However, there is sufficient room for improvement in efficiency of air intake through the slits of the related-art axial fan described above. This point will now be described below with reference to FIG. 16.
An axial fan illustrated in FIG. 16 includes a housing 1 whose external shape is substantially square. Each side of the housing 1 includes a slit group 4 made up of a plurality of slits 4a to 4k defined therein. Each of the slits 4a to 4k in each slit group 4 is arranged to extend through the corresponding side of the housing 1 from an inner circumferential surface 2 to an outer circumferential surface 3 of the housing 1. The slits 4a to 4k in each slit group 4 are arranged to extend in parallel or substantially in parallel with one another, and in a direction perpendicular to the corresponding radially outer side of the housing 1. With this arrangement of the slits, each slit group 4 inevitably includes a region (i.e., a region P shown in FIG. 16) where a direction (hereinafter referred to as an “air intake direction”) W of air intake through the slits differs considerably from a rotation direction R of an impeller (not shown). Note here that the impeller draws in air in a direction along the rotation direction R of the impeller. In the regions P mentioned above, the air intake direction W differs considerably from the direction in which the impeller draws in air. Therefore, in the regions P, air that has come in through the slits tends to be less easily drawn in by the impeller. Therefore, the regions P cause reductions of air intake efficiency of the fan as a whole.